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Genetic Linkage is the tendency of short chromosomal segments to be inherited intact from parent to offspring. Certain combinations of these alleles may be preserved over a large number of generations and become quite frequent in the population. Linkage Disequilibrium is the excessive co-occurrence of certain combinations of alleles in the same person because of tight linkage.
LD decays at a rate proportional to the recombination fraction between the two loci in LD and the number of generations. This phenomenom has traditionally been exploited to estimate the time elapsed since the initial event that established LD in the ancestral population.
More recently, LD has become an increasingly important tool for the mapping of genetic loci as the Human Genome Project is rapidly identifying many functional loci in the human genome, together with numerous polymorphisms in and around these functional DNA sequences. LD occurs in populations as a consequence of many factors including mutation, random genetic drift, selection of single or linked alleles and population admixture. As different evolutionary origins may produce different genomic patterns among selectively neutral loci, having an impression of the LD for a given population can greatly facilitate genetic studies that are centered around this phenomenon.
Because it evolved from a limited number of founders and the population grew through natural expansion rather than immigration, Newfoundland is an enriched genetic population. Coupled with this, the relative geographic isolation that existed for many years further limited the population admixture. As a result, Newfoundland has important advantages for the mapping of susceptibility alleles as compared to more admixed populations. It is for these reasons (founder effect and limited allelic heterogeneity) that we believe the Newfoundland population lends itself to map genes using a more novel approach that will be based on the strength of the LD for this population.
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